Fuse construction



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FUSE CONSTRUCTION Filed March 9, 1959 2 Sheets-Sheet 1 Nn E. .M AAW d m F 3 Ea B597 ,effi

Nov. 22, 1960 E. i.. SANKEY FUSE CONSTRUCTION Filed March 9, 1959 2 Sheets-Sheet 2 Z777@ '22 .Seconds 5 5U 500 7M .5G00

Carrent rz AVM/@eres INVENTOR. ,du/ara San/@y BY ffl@ f #tra freely United States Patent O FUSE CONSTRUCTION Edward L. Sankey, (lak Creek, Wis., assignor to McGraw- Edison Company, Milwaukee, Wis., a corporation of Delaware Filed Mar. 9, 1959, Ser. No. 797,911

Claims. (Cl. 2004120) This invention relates in general to fuse construction and more particularly relates to a fuse construction ernploying a hermetically sealed fusible element disposed within an insulating tube, the whole construction being adapted to be immersed in a d'electric liquid or high pressure gas mediums associated with the electrical equipment it is designed to protect.

The time-current characteristics of fuse elements disposed in a dielectric liquid med'um or a high pressure gas medium associated with transformers, reclosers, and the like and directly exposed to said liquid or high pressure gas mediums have a different time-current characteristic than the same fuse element shows when it is disposed in an ordinary pressure gaseous medium such as air. The dielectric liquid tends to cool the fuse element and make a speed ratio of the fuse links which is considerably faster than is desirable.

It is easier to design fuse links in a gaseous medium at atmospheric pressure having the desired characteristics (time-current curve) than it is to design a similar fuse link to be in direct contact with the dielectric fluid.

yIt is thus an object of this invention to provide a fusible element which is manufactured in ordinary air or other gaseous dielectric medium there being a hermetically sealed container means therearound which maintains the desired and uniform time-current characteristics regardless of the medium in which it is disposed which affords uniformity for coordination purposes.

lt is a further object of this invention to provide a fuse structure which is designed to be immersed in a dielectric fluid or high pressure gas medium associated with the electrical equipment it is to protect, the time-current characteristcs being those of an ordinary pressure gaseous medium while utilizing the dielectric liquid or high pressure gas to cool and extinguish the arc upon rupture of the hermetically sealed container means.

It is a further object of this invention to alford a fuse construction which has an insulating tube capable of evolving arc extinguishing gases (such as horn bre) surrounding the hermetically sealed container means whereby upon rupture of the fusible element within the container means, the combination action of the dielectric ilud and the gas generated by the tube speedily eX- tingu'sh the are generated by the breakdown of the aforesaid fusible element.

It is a further object of this invention to provide a fuse construction which is well adapted to mass manufacture techniques, used as a minimum number of components, and is otherwise well adapted for the purposes for which it was designed.

The novel features wh'ch are characteristic of the invention are set forth with particularity in the appended claims. The invention itself, both as to its o-rganization and in its method of operation together with additional objects and advantages thereof will best be understood by the follow'ng description of specic embodiments when read in connection with the accompanying drawings in which:

Fig. l is a vertical sectional view of the novel fuse construction shown immersed in a dielectric tluid;

Fig. 2 is an enlarged fragmentary sectional v1ew o f a portion of the fuse assembly shown in Fig. 1, said view being taken at the time when the fusible element 1s rupturing due to an overload current;

Fig. 3 is a semidiagrammatic view showing one d1sposftion of the fuse assemblies in a circuit for protection of a potential coil in a recloser;

Fig. 4 is a sectional view of an alternate embodiment of fuse construction; i

Fig. 5 is a semidiagrammatic view showing the dispos1- tion of the alternate fuse assembly of Fig. 4 in a transformer circuit when immersed in the dielectric liquid of a transformer tank; and

Fig. 6 is a graph showing the typical time-current characteristics of the fuse construction under discussion under varying cond'tions of air and oil mediums. (Air and oil representing typical examples of gas and liquids to which fuse links may be exposed.)

The fuse assembly 10 is primarily designed for immersion in a dielectric liquid med'um, for example an oil filled housing for electrical apparatus it is to protect. One such apparatus is a recloser 11 shown semidiagrammatically where a pair of fuse assemblies 10 are connected in series with a potential coil 13 of a recloser. (The fuses are in series with the potential coil, but the coil is shunted across the line-the recloser also has coils connected in series with the line but these are not protected by the fuses under discussion.) Suitable dielectric is disposed in surrounding relation to the fuse assembly 10 and to the rest of the electrical components, said dielectric being denominated with the reference numeral 15. A housing surrounds the entire electrical apparatus and here is shown semidiagramrnatically by the reference numeral 14.

Another electrical apparatus which a similar fuse assembly 10 is designed to be associated with is shown in Fig. 5, said apparatus being a transformer 12 having an outer housing 16, primary and secondary windings 17, the primary of wh'ch is grounded to the housing at 18. Conductors 19 and 20 extend between the primary winding and a bushing 21, the fuse assembly 10' being disposed intermediate the two conductors 19 and 20 on the input side of the primary winding. Of course, other practices may be followed depending on the type of transformer or other equipment to be protected.

Now to the fuse assembly per se. Attention is directed to Figs. l `and 2. The fuse assembly 10 essentially comprises an elongated hollow insulating tube 23 having a central bore closed at the upper end by a circular plug 24 which is held in place by a drive screw or drive pin 25. The plug 24 provides a directional effect for expulsion action as shall become apparent hereinafter. it" desired, the fuse may be mounted horizontally and no plugs used. A suitable upper lead conductor 26 extends through the plug 24 and has attached thereto interiorly of the tube 23 a short lead wire 29.

Extending through the open bottom end 33 of the fuse turbe 23 is a lead wire 28 having a connecting end surface 27 exterior of the tube. The lead wire 28 is surrounded at its upper end by a small metal tube 30 which is iixedly mounted therearound `as by crimping. A suitable tension spring 31 is disposed in surrounding relation to wire 28 and metal tube 3d and engages the latter at its upper end to bias lead wire 2S in a downwardly direction as shown in the drawings. The bottom-most end of tension spring 31 is enlarged so as to engage the end surface of an openended protective metallic insert 33a to bias the wire 28 in a downwardly direction, while permitting free access of the dielectric fluid l5 to the interior of the tube 23.

Electrically and physically attached at the bottom and yupper ends of wire conductors 29 and 28 respectively is a hermetically sealed frangible container means 34. The container means 34 comprises a hollow insulating tube 35 made of glass, ceramic or the like which is frangible when contacted by anarc. Attached to the upper end and lower end of insulating tube 35 are conducting metallic end caps 36 which may be soldered to wires 2S and 29 as shown. To insure a tight hermetic seal between the metal caps and the glass tube, epoxy resin 37 is lplaced around the margin of the caps 36 to prevent ingress and egress of dielectric fluid to the interior of the tube 3S. Other suitable sealing means, of course, may be provided.

Disposed within the fuse container means 34 is a fusible element 38 which is biased downwardly (only in the case of soldered joint links) by a suitable tension spring 39. Element 38 can be any well known fuse element construction such as tin, silver wire, soldered joint, etc. Fusible element 38 is in turn electrically connected to the metallic end caps 36 to receive current therethrough.

When an overload current goes through the fusible section 38, the fusible section 38 softens or melts under the heat and parts. An arc is then generated between the ends of the ruptured fusible element 33, said arc causing a breakdown of the frangible walls of the glass tube 35. The arc is then cooled by the dielectric l and in the ernbodirnent shown by the generation of gas from the tube 23. Pressure and turbulence is also developed in the interior of the tube 23 due to heat of the arc. The entire bottom portion of the fuse assembly is biased downwardly by tension spring 31 which tends to elongate the arc. If

desired, the pressure generated by the arc can supplant spring 31. Thus, the combination of the gas pressure and turbulence generated, the cooling by the dielectric material, and elongation of the arc extinguishes same. The pressure build up within the insulating tube provides an expulsion action-sweeping out the ionized and conducting gases and thus also helping to extinguish the arc.

As noted in the objects, it is particularly desirable to manufacture the fuse elements under dry conditions to maintain desired time-current characteristics. To this end, it is advantageous to completely seal the container ymeans 34 so that the time-current characteristics remain uniform and unaffected by the dielectric medium of the device in which the fuse is used. Further, the timecurrent characteristics of the fusible element 3S is then entirely independent of the medium in which it is disposed. This independence of characteristics is obtained because the fusible section is spaced from the dielectric medium by the sealed container means.

The alternative embodiment shown in Fig. 4 is shown for example purposes only, adapted for use in a transformer and is substantially similar to that shown in Figs. 1 and 2. The essential diilerences are that the upper conductor 40 has necked down portion 4l which attaches directly to the end cap 36 of the container 34. Further, there is no biasing spring on the bottom of the assembly, the end of the conductor 42 dropping out of the fuse tube 23 under the influence of gravity and the expulsion action of gases formed or heated by the arc. The fuse tube 23 per se is formed with a suitable groove 43 for engagement with a suitable bracket mountingly attached to a transformer (or other device) as shown in Fig. 5.

Fig. 6 shows a graph of typical time-current characteristics of the fuse under varying conditions. Fig. 6 represents only one fusible element. Numerous elements may be used which would alter the slope and location of the curves, but the same general relationships would still hold for any given element. The curve identied as S is illustrative of the time-current characteristics of a hermetically sealed unit 34 with a dual element (soldered joint type) fusible section such as shown in Fig. 1 or 4 when disposed within an insulating tube and the entire unit immersed in oil. The identical fusible element when disposed in oil alone (without container 34) is shown by the curve denominated by the letter T. The curves Y and Z are indicative respectively of a single element fuse link (not shown), the curve Y indicating the slower timecurrent characteristics of a hermetically sealed fuse link when enclosed as shown in Figs. l or 4, and the curve Z being the identical link when no hermetic seal is employed and the fuse element is simply immersed in oil.

Although specic embodiments of the invention have been shown and described, it is with full awareness that many modifications thereof are possible. The invention, therefore, is not to be restricted except insofar as is necessitated by the prior art and by the spirit of the appended claims. Y

What is claimed as the invention is:

l. A protective device for a transformer comprising, in combination, housing means surrounding the transformer to be protected, conductor means being connected at one end to said transformer and at the other end to a source of electrical power, liquid dielectric means disposed Within said housing and fuse means disposed within said housing intermediate the ends of said conductor means and immersed in said liquid dielectric, said fuse means comprising gas evolving outer tube means permitting free access of the dielectric liquid therewithin, hermetically sealed frangible container means disposed within said gas evolving outer tube means, and fuse link means disposed within said sealed container means and electrically connected to said conductor means so that on occurrence of a predetermined electrical condition, said fuse link means will rupture within said sealed container means, causing the latter to rupture to afford cxtinguishment of an arc by the combination action of the gases evolved from said gas evolving outer tube means and liquid dielectric means while maintaining the timecurrent characteristics of the environment of the sealed container means.

2. A protective device for electrical apparatus comprising, in combination, fuse means adapted to be immersed in a liquid dielectric, said fuse means comprising gas evolving insulating tube means having an opening permitting free acess of the dielectric liquid therewithin, hermetically sealed frangible container means disposed within said gas evolving insulating tube means, and fuse link means disposed within said sealed container means so that on occurrence of a predetermined electrical condition, said fuse link means will rupture within said sealed container means, causing the latter to rupture to afford extinguishment of an arc by the combination action of the gases evolved from said gas evolving insulating tube means and liquid dielectric means while maintaining the time-current characteristics of the environment of the sealed container means.

3. A protective device for electrical apparatus comprising, in combination, housing means surrounding the electrical apparatus to be protected, conductor means being connectable at one end to said apparatus and at the other end to a source of electrical power, liquid dielectric means disposed within said housing, and fuse means disposed within said housing intermediate the ends of Said conductor means and immersed in said liquid dielectric, said fuse means comprising gas evolving tube means permitting free access of said liquid dielectric therewithin, hermetically sealed frangible container means disposed within said gas evolving tube means, and fuse link means disposed Within said sealed container means and electrically connected to said conductor means so that on occurrence of a predetermined electrical condition, said fuse link means, While maintaining the time-current characteristics of the environment of the sealed container means, will rupture within said sealed container means causing the latter to rupture to afford extinguishment of an arc by the combination action of said gas evolving tube means and said liquid dielectric means.

4. A protective device for electrical apparatus comprising, in combination, fuse means disposed within a liquid dielectric, said fuse means comprising rst conining means permitting free access of said liquid dielectric therewithin, hermetically sealed frangible container means including a gaseous dielectric material disposed within said rst confining means, and fuse link 'means disposed within said sealed container means so that on occurrence of a predetermined electrical condition, said fuse link means, while maintaining the timecurrent characteristics of said gaseous dielectric material within the sealed container means, will rupture within said sealed container means causing the latter to rupture to atlord extinguishment of an arc by the action of said rst conning means and first liquid dielectric means.

5. A device in series with a bushing and the primary winding of a transformer for electrically protecting the transformer comprising, in combination, housing means surrounding the transformer to be protected, conductor means being connected at one end to said primary winding of said transformer and at the other end to a source of electrical power, liquid dielectric means disposed within said housing, and fuse means disposed within said housing intermediate the ends of said conductor means and immersed in said liquid dielectric, said fuse means comprising gas evolving insulating tube means permitting free access of the dielectric liquid therewithin', hermetically sealed frangible container means disposed within said tube means, fuse link means disposed within said sealed container means and electrically connected to said conductor means, means connected to said fuse link means and disposed within said container means for downwardly biasing said fuse link means, whereby on occurrence of a predetermined electrical condition, said fuse link means, while maintaining the time-current characteristics of the environment of the sealed container means will rupture within said sealed container means causing the latter to rupture to aiord extinguishment of an are by the combination action of said gas evolving tube means and liquid dielectric means.

References Cited in the file of this patent UNITED STATES PATENTS 933,787 'Rowe et al. Sept. 14, 1909 959,552 Kintner et al May 3l, 1910 2,727,961 Smith Dec. 20, 1955 FOREIGN PATENTS 303,090 Great Britain Dec. 28, 1928 

